A tandem drive axle is typically used to drive rear wheels on a heavy-duty commercial vehicle, such as a tractor-trailer vehicle, for example. The tandem drive axle includes a forward drive axle and a rear drive axle that are connected by an interconnecting driveshaft. The tandem drive axle includes an inter-axle differential assembly that allows speed differentiation between the forward drive axle and the rear drive axle. The inter-axle differential assembly provides speed differentiation between driving input to a forward differential gear assembly for the forward drive axle and driving input to a rear differential gear assembly for the rear drive axle as needed.
A typical inter-axle differential assembly includes a rear side gear, a plurality of inter-axle differential pinion gears supported on a spider, a forward side gear, and an inter-axle differential housing assembly. An input shaft drives the spider. The forward and rear side gears are in meshing engagement with the plurality of inter-axle differential pinion gears. The forward side gear is coupled to drive a helical gear that drives the forward differential gear assembly. The spider and the plurality of inter-axle differential pinion gears are enclosed within the inter-axle differential housing assembly.
The forward drive axle includes an axle housing that includes a center bowl portion that receives the inter-axle differential assembly and the forward differential gear assembly. The forward differential gear assembly is enclosed within a gear housing to form a carrier assembly. The inter-axle differential housing assembly is positioned within the carrier assembly and the carrier assembly is bolted to the axle housing. An input yoke couples a vehicle driveshaft to the input shaft of the inter-axle differential assembly to provide driving input into the forward drive axle.
This configuration has some disadvantages. One disadvantage is that the inter-axle differential housing assembly significantly increases the weight of the inter-axle differential assembly. This adversely affects fuel economy. Further, the need for the inter-axle differential housing itself increases overall component cost and assembly time.
Another disadvantage is that this configuration can have a relatively large standout dimension. Standout is defined as a distance from a machined surface of the axle housing, adjacent the center bowl portion, to an end of the input yoke. Standout adversely affects driveline angles. The greater the standout, the greater the driveline angle. Greater driveline angles can adversely affect component wear.
It would be beneficial to provide an inter-axle differential assembly that eliminates the inter-axle differential housing assembly and reduces standout. The inter-axle differential assembly should be lightweight and easy to assemble, as well as overcoming any other above-mentioned deficiencies in the prior art.